There are different use cases for rbm :

easy package creation::
        You have multiple people in your team working on the developement
        of your software, and you want them all to be able to build a
        package from any git or mercurial revision using a simple command.

continuous integration::
        Automatically build packages for the latest version of you
        software available in your git or mercurial repository.

multi distro packaging::
        You want to create packages for your software for different
        distributions.

regular package maintainance::
        You maintain a lot of packages for software available in git or
        mercurial repositories, and you want to avoid the boring tasks of
        manually creating / downloading tarballs, checking signatures,
        updating package versions and want to automate as much as possible.

